The designs of intake manifolds used with internal combustion engines are becoming more flow efficient. As a result, the air flow through the intake system is becoming more laminar under certain engine operating conditions, especially those that employ lower flow rates. This can present concerns relative to a laminar air stream in the air intake system downstream from the throttle plate. This loss of flow turbulence results in an increased difficulty in properly mixing gases from engine systems such as the exhaust gas recirculation (EGR) system, the positive crankcase ventilation (PCV) system and the gas vapors absorbed from the fuel tank ventilation canister (EVAP) that are fed into the main airstream of the manifold downstream of the throttle body. Good mixing of the metered gasses in the main airstream is important for ideal engine operation.
The loss of flow turbulence also creates an increased concern over induction system noises, such as hoots and whistles (NVH), at the low air flow (idle and off idle) operating conditions. The noise can be generated from the airstream flow if resonance occurs from the connecting passages of the incoming flow of gases intersecting the main airstream (a "pop bottle" effect).
Furthermore, vehicle packages are becoming more restrictive and the past tradition of always providing a "positive drainback" away from the throttle plate to prevent moisture and sludge contamination on the throttle plate is an increasing challenge. Moisture and backflow of contaminants from the downstream air intake passage to the throttle plate can potentially create concerns with moisture freezing on the throttle plate or sludge building up on the throttle plate from the contaminates.
Hence, there is a desire to correct these concerns in an economical manner, while not greatly impacting a vehicle's weight nor increasing the room needed in the engine compartment for the air induction system, so as to avoid air induction system packaging concerns.